1. Field of the Invention
The present invention relates to a method of metallizing a surface of sintered ceramic containing a silicon compound as its component or an additive. More particularly, it relates to a method of forming a manganese layer or manganese-containing alloy layer of good adhesion on the desired surface of ceramics containing a silicon compound which is reactable with manganese to produce manganese silicide at a temperature lower than a melting point of manganese and in a short time, and a method of joining a film or a sheet of another metal onto the manganese layer or manganese alloy layer.
The metallized ceramics manufactured according to the present invention are put into various uses a direct materials and intermediate materials including substrates for semiconductor devices, electronic parts, mechanism parts, structural materials, etc.
2. Description of the Prior Art
Methods of metallizing sintered ceramics bodies, especially sintered alumina ceramics, have been known for a long time. The metallization of ceramics is very important in the provision of electrodes for ceramics capacitors, the provision of insulating sealing in electron tubes etc., the technology of joining semiconductor elements in semiconductor devices, the technology of wiring on the substrates of semiconductor devices, and so forth.
Regarding oxide-type ceramics such as alumina and beryllia, research has been conducted for several years, and there are various metallization methods. For example, as to the alumina ceramics, there is a method in which a mixed paste consisting of manganese powder and molybdenum powder is applied onto the ceramics and then baked. There have also been proposed pastes in which titanium hydride, aluminum oxide, silicon oxide, calcium oxide, etc. are mixed into the aforementioned powder (Japanese Laid-open Patent Application No. 55-113683).
The aforecited patent application discloses, in connection with a method of metallizing silicon carbide ceramics, a powdery metallizing composite which contains 100-10 parts by weight of at least one of group-IVa, -Va, -VIa and -VIIa metals and 0-90 parts by weight of at least one of group-Ib, -IIb, -IIIb, -IVb and -VIII metals. In the light of the description of the patent application including examples, the composite is applied onto a silicon carbide ceramic in the form of a paste and is heated so as to form a metal film on the surface of the ceramic. The paste is fired without liquefying (melting) during heating (at 1000.degree. C.-1800.degree. C.). For instance, a paste consisting of Cu powder (20 weight-%) and Mn powder (80 weight-%) is applied onto a silicon carbide ceramic and then baked in vacuum. In this regard, it is concluded that the metallized state is not good at a baking temperature of 800.degree. C. In the specification of the patent application, the heating period of time for baking the paste is not clearly mentioned. Since, the diffusion of metal is utilized, the heating will require a long time.
A method wherein an alumina ceramic is metallized by the use of a paste consisting of molybdenum (80%)-silica (7-3%)-manganese dioxide (3-2%)-tungsten (5-15%), is disclosed in Japanese Laid-open Patent Application No. 54-58714. Herein, it is described that the metallizing temperature is 1370.degree. C. and that the metallization is effected by diffusion bonding.
There has also been known a method wherein silicon nitride ceramics are metallized by diffusion bonding at 1550.degree. C. with a paste which contains tungsten powder and manganese powder (Japanese Laid-open Patent Application No. 55-51774).
Any of these metallizing methods require heating the ceramics and the paste at a high temperature for a long time.
Alumina ceramics are used in large quantities chiefly as electronic parts and electronic materials. Silicon carbide ceramics have applications in the same fields as those of alumina ceramics, and may be used as industrial machine materials for gas turbines, sealing, etc.
If silicon carbide ceramics and alumina ceramics would be easily metallized at a lower temperature in a shorter time, undesirable thermal stresses on the ceramics would be reduced, and a saving of thermal energy as well as an enhancement of mass-producibility ought to be expected.
According to our recent researches, it has been revealed that when conventional pastes containing molybdenum powder or tungsten powder and optionally containing manganese powder are coated and fired on a ceramic substrate, an electric resistivity on the ceramic surface which has no coating of a fired paste or a metallic film is decreased due to diffusion of manganese or a deposition of vaporized molybdenum thereon. Because of the decrease in surface resistivity, it has also been observed that there is an increase in leak current on the ceramic surface. From the above point of view, it is desirable to carry out a metallization treatment at as low temperatures as possible in a short time.